Conventionally, for a shaft-bearing holding structure configured in a disk-rotating motor which is used in a disk-driving device which requires a thinning and size-reduction, a variety of shaft-bearing holding structures such as a shaft-bearing holding structure which uses a sintered member of the same material as a shaft-bearing, a shaft-bearing holding structure which uses a cutting processing member made of brass, and the like have been suggested. Also, in order to cope with a recent trend of the rapid cost-down, it is required to configure the shaft-bearing holding structure by combining members as inexpensive as possible. At the same time, the needs for reliability are also increased. Particularly, regarding a shaft-bearing holding structure for vehicle mount, the shock resistance and the vibration resistance are important requirements. In addition, the requirement for the assembling precision becomes also stricter so as to cope with a large capacity medium such as Blu-ray.
As a representative example of a configuration of combining inexpensive members while securing high reliability, a structure has been also suggested in which a shaft-bearing holding mechanism is configured only by metal press processing products.
For example, conventionally, as such disk-rotating motor, a disk-rotating motor shown in FIG. 5 has been suggested (for example, refer to Patent Document 1). The disk-rotating motor includes a rotor section 101 and a stator section 102. Burring processing is implemented at a substantial central part of a bracket 103 of the stator section 102. The burring part 104 includes, at an inner diameter part thereof, a shaft-bearing 106 rotatably bearing a shaft 105 and functions as a shaft-bearing housing. Also, the burring part 104 is provided at its entrance with a thrust cap 107 which supports load of the rotor section 101 in a thrust direction and is press-fitted and fixed while providing a thrust plate 108 having wear resistance.
Also, a conventional disk-rotating motor shown in FIG. 6 includes a rotor section 109 and a stator section 110. Burring processing is implemented at a substantial central part of a bracket 111 of the stator section 110. A cup-shaped shaft-bearing housing 113 integrally having a bottom surface at one end side of a cylindrical part is press-fitted and fixed to the burring part 112. The shaft-bearing housing 113 is fitted at an inner diameter part thereof with a shaft-bearing 115 for bearing a shaft 114 and supports load of the rotor section 109 in a thrust direction while providing a thrust plate 116 having wear resistance on a bottom surface part thereof (for example, refer to Patent Document 2).
Also, a conventional disk-rotating motor shown in FIGS. 7A and 7B includes a rotor section 119 and a stator section 120. A bracket 121 of the stator section 120 is formed at a substantial central part thereof with a recess part 123 into which an outer periphery of a shaft-bearing housing 122 is fitted. A bottom surface thereof supports a shaft 125 via a thrust plate 124. Also, as shown in FIG. 7B, the recess part 123 is formed therein a groove part 126 into which a base end of the shaft-bearing housing 122 is connected. A projecting part 127 for welding is formed in the groove part 126, so that the bracket 121 and the shaft-bearing housing 122 are welded and tightened (for example, refer to Patent Document 3).
In the meantime, recently, for the disk-rotating motor which is used in a disk-driving device, the cost-down, the high reliability and the high precision are required in addition to the size-reduction and the thinning
However, in the shaft-bearing holding structure shown in FIG. 5, as the motor is smaller and thinner, an axial length of press fitting the thrust cap 107 is shortened, so that the tightening strength is lowered. Hence, as the motor is made to be smaller, there occurs a problem where the holding strength becomes insufficient in the support of the load of the rotor section 101 in the thrust direction. Even when the adhesion were also used for fixing, an adhesion area is decreased. Hence, it is not possible to expect the sufficient strength. Also, the adhesive flows to a shaft-bearing, so that the reliability may be degraded. Also, the fixing by the welding is difficult to implement due to its structural reason. In view of the assembling precision, particularly a distance variation from a motor fixing position to a rotational center upon the assembling, according to the method of press fitting an outer diameter part of the shaft-bearing, since the outer diameter part of the shaft-bearing is worn upon the press fitting and the coaxial precision between the outer diameter part and the inner diameter part is accumulated, there is a limit in securing the high precision.
Also in the shaft-bearing holding mechanism shown in FIG. 6, as the motor becomes smaller and thinner, the lengths of the shaft-bearing housing 113 and the bracket 111 in the press-fitting axial direction are shortened and the tightening strength is decreased. In this configuration, in order to support the load of the rotor section 101 in the thrust direction, like the shaft-bearing holding mechanism shown in FIG. 5, it is necessary to support an outer diameter step part 117 of the shaft-bearing housing 113 with a burring part end face 118 of the bracket 111. When it is compulsory to make the motor smaller and thinner, it is difficult to satisfy the tightening strength of the shaft-bearing housing 113 and the shaft-bearing 115 fitted in the inner diameter thereof and the tightening strength of the shaft-bearing housing and the bracket 111 at the same time.
Also in the shaft-bearing holding structure shown in FIG. 6, the fixing by the welding is difficult to implement due to its structural reason, like the configuration shown in FIG. 5. Also, the fixing by the adhesion is not useful because the adhesive may flow to a lower surface of the bracket. Also, like the configuration shown in FIG. 5, the distance variation from the motor fixing position to the rotational center has a limit in securing the high precision because a variation such as plate thickness of the shaft-bearing housing is accumulated.
In any case, it is clear that as the motor becomes smaller and thinner, it is difficult to secure the tightening strength only by the press fitting fixing. Hence, a structure is preferable in which the high support rigidity for the load of the rotor section in the thrust direction is secured and the shaft-bearing housing employs a tightening method, other than the press-fitting fixing only, which can be performed based on the high reliability.
Compared to the above, the shaft-bearing holding structure shown in FIG. 7 is fitted and held in the recess part 123 of the bracket 121. Thereby, since the bracket 121 axially supports the shaft 125 and secures the support rigidity for the load of the rotor section 119 in the thrust direction, the high reliability can be secured. Also, according to this conventional shaft-bearing holding mechanism, the groove part 126 for fitting the shaft-bearing housing 122 is further formed in the bottom surface of the recess part 123 for fitting with the shaft-bearing housing 122, which is formed at the central part of the bracket 121. Thereby, this conventional shaft-bearing holding mechanism has a function of preventing sputters, which are generated upon the fixing by the welding, from being introduced into the shaft-bearing or a function of preventing the adhesive, which flows out upon the fixing by the adhesion, from being introduced, thereby enabling the tightening by the welding or adhesion. However, only the base end of the shaft-bearing housing 122 is tightened. Therefore, when the vibration is applied, an opposite end face of the shaft-bearing housing 122 may be elastically deformed. Thus, it cannot be said that the reliability is very high in a device for vehicle mount in which the vibration is excessively generated.
Also, according to the shaft-bearing holding mechanism shown in FIG. 7, since the distance variation from the motor fixing position to the rotational center completely depends on the precision of an assembly jig, tolerances of parts are not accumulated, which is favorable. However, there is a limit in securing the high precision in view of the wear of the jig or maintenance precision while considering the mass production.